There was no tsunami damage "though there may be slight sea level changes from now on," it said, referring to the areas affected by the advisory -- the Okinawa Islands, the Amami Islands and the Tokara Islands.

The quake was felt on Okinawa, with shaking that lasted about 15 seconds, said Lt. Col. Daniel King of the U.S. Pacific Command. He told CNN that commanders in Japan and Hawaii were trying to get damage and casualty reports from U.S. military stations on Okinawa, but had heard nothing in the immediate aftermath.

About 20,000 U.S. troops -- mostly Marines, along with Navy and Air Force personnel -- are stationed on eight bases on Okinawa, he said.